The present invention relates to the field of prostheses. More particularly it relates to the field of prostheses, used to replace surgically removed bone segments.
In the treatment of diseases it is sometimes necessary to remove and replace a segment of bone. Such is frequently the case in treatment of bone cancers. Replacement of the diseased segment with a prosthesis is preferable to amputation.
The state of medical art has developed to the point that, when the patient is fully grown, a fixed size prosthesis can be inserted to replace the removed bone segment. For example, hips, and segments of fibula, tibia, ulna, radius and humerus are commonly replaced in this way. However, when the patient is a child, an extendible prosthesis is necessary to maintain equality of limb length as the child grows.
Two types of extendible bone prostheses have been used in recent years. One type has an internal gear and worm mechanism. To lengthen this prosthesis requires turning the gear with a special key. The other type is extended by inserting ball bearings of a standard size into a telescoping shaft thus it can only be extended in quantum increments and cannot be shortened once extended. Both these prostheses require major invasive operations for lengthening and since the entire compressive load is supported by metal, they are susceptible to fatigue failures.
Other designs utilizing an electromotor with an inductive power supply and a rotating magnetic field have been proposed. The main difficulty with these proposals is the difficulty of producing enough force to extend the limb.
An extendible bone prosthesis that did not depend on a metal to support the compressive load and which did not require major invasive surgical techniques for operation would satisfy a long felt need in the field of pediatric orthopaedic surgery.